This invention relates to tackified crosslinkable polydiorganosiloxane oligourea segmented copolymer, in particular to copolymers that are useful as pressure-sensitive adhesives, hot melt adhesives, vibration damping compositions, as well as articles made from such copolymers.
Pressure-sensitive adhesive tapes have been used for more than half a century for a variety of marking, holding, protecting, sealing and masking purposes. Pressure-sensitive adhesive tapes comprise a backing, or substrate, and a pressure-sensitive adhesive. Pressure-sensitive adhesives are materials which adhere with no more than applied finger pressure and are aggressively and permanently tacky. Pressure-sensitive adhesives require no activation, exert a strong holding force and tend to be removable from a smooth surface without leaving a residue. In some applications, interesting pressure-sensitive adhesives are silicone based adhesives.
Traditionally, polydiorganosiloxane pressure-sensitive adhesives have been made in solution. Conventional solvent based polydiorganosiloxane pressure-sensitive adhesives are generally blends of high molecular weight silanol functional polydiorganosiloxanes, i.e., polydiorganosiloxane gums, and copolymeric silanol functional silicate resin, i.e., MQ resins, which comprise R3SiOxc2xd units and SiO{fraction (4/2)} units. In order to obtain the desired adhesive properties, it has been necessary to react the copolymeric silicate resin with the polydiorganosiloxane. Improvements in such pressure-sensitive adhesive properties are achieved when the copolymeric polydiorganosiloxane resin and polydiorganosiloxane are intercondensed, providing intra- and inter-condensation within the adhesive. This condensation step requires 1) the addition of a catalyst, 2) reacting the copolymeric polydiorganosiloxane resin and polydiorganosiloxane in solution, and 3) allowing the reaction to take place over a period of time at elevated temperature.
Solutions of intercondensed polydiorganosiloxane pressure-sensitive adhesives, are generally applied to a backing, heated to remove solvent, and crosslinked, if necessary, to improve physical properties. If crosslinking is needed, peroxide catalysts are commonly used. Disadvantages of solution applied polydiorganosiloxane pressure-sensitive adhesives include the need for elaborate drying ovens to remove solvent, and if crosslinking is required, ovens which operate at temperatures greater than 140xc2x0 C. are needed to initiate diaryl peroxide crosslinking catalysts. Such high oven temperatures limit the substrates useful in making pressure-sensitive adhesive tapes to those which can withstand the elevated temperatures.
In the medical field, pressure sensitive adhesive tapes are used for many different applications in the hospital and health areas, but basically they perform one of two functions. They are used to restrict movement, such as in various strapping applications, or they are used to hold something in place, such as a wound dressing. It is important in each function that the pressure sensitive adhesive tape be compliant with and non-irritating to the skin and adhere well to the skin without causing skin damage on removal.
In recent years, pressure sensitive adhesives have been used in transdermal patch applications as drug transport membranes or to attach drug transport membranes to skin. Although there is continued development of new drugs and the need for different transport rates of existing drugs, pressure sensitive adhesives are still needed that can transport such drugs at various rates. Furthermore, there is a continuing need to adhere new drug transport membranes to skin during a treatment period.
In the automotive industry, there are applications that remain unaddressed by current tape products. One such application relates to automotive paints and finishes that are formulated for environmental conservation, recyclability, enhanced appearance, improved durability, as well as resistance to environmental sources of contamination. Painted substrates using these new formulations are difficult to adhere to with current tape products. Another application involves mounting thermoplastic polyolefin automotive body side moldings.
Similarly, early electrical tapes were black friction tapes, and the adhesive was soft and often split when unwound. Current electrical tapes have a layer of a pressure sensitive adhesive applied to a plasticized polyvinyl chloride backing or a polyethylene or rubber film backing. Electrical tape is used to insulate, hold, reinforce and protect electrical wires. Other uses include providing a matrix for varnish impregnation, identifying wires in electrical circuitry, and protecting terminals during manufacture of electrical circuit boards. Electrical tape, should be stretchable, conformable and meet nonflammability requirements.
Preformed pavement marking materials include pavement marking sheet materials and raised pavement markers that are used as highway and pedestrian crosswalk markings. They are often reflective and strategically oriented to enhance reflective efficiency when illuminated by vehicle headlamps at night. The marking materials must adhere to a variety of surfaces such as concrete or asphalt, that may be cold, hot, oily, damp, rough or smooth. Present pavement marking adhesive generally have inadequate initial bonding or inadequate permanent bonding to roadway surfaces that are illustrated by five problem areas: (1) limited adhesive tack at cold temperatures resulting in a narrow application window, (2) reduced durability under shear or impact causing difficult removal of temporary markings, (3) low molecular weight fractions in the adhesives on removable markings that stain light colored concrete surfaces, (4) limited ductility allowing raised markers to sometimes shatter upon impact by vehicle tires and (5) insufficient elasticity to fill in gaps between markers and rough road surfaces, thus often leading to premature detachment of the marker from the roadway surface.
Hot melt adhesives are compositions that can be used to bond nonadhereing surfaces together into a composite. During application to a substrate, hot melt adhesives should be sufficiently fluid to wet the surface completely and leave no voids, even if the surface is rough. Consequently, the adhesive must be low in viscosity at the time of application. However, the bonding adhesive generally sets into a solid to develop sufficient cohesive strength to remain adhered to the substrate under stressful conditions.
For hot melt adhesives, the transition from fluid to solid may be accomplished in several ways. First, the hot melt adhesive may be thermoplastic that softens and melts when heated and becomes hard again when cooled. Such heating results in sufficiently high fluidity to achieve successful wetting. Alternatively, the hot melt adhesive may be dissolved in a solvent or carrier that lowers the viscosity of the adhesive sufficiently to permit satisfactory wetting and raised the adhesive viscosity when the solvent or carrier is removed. Such an adhesive can be heat activated, if necessary.
Damping is the dissipation of mechanical energy as heat by a material in contact with the source of that energy. The temperature range and frequency range over which damping occurs can be quite broad, depending upon the particular application. For instance, for damping in tall buildings that experience wind sway or seismic vibrations, the frequency range can go to as low as about 0.1 Hertz (Hz) up to about 10 Hz. Higher frequency damping applications can be those such as for computer disk drives (on the order of 1000 Hz) or higher frequency applications (10,000 Hz). Furthermore, outdoor damping applications can be exposed to a wide range of temperature and humidity conditions.
While the performance of a surface layer damping treatment depends largely on the dynamic properties of the viscoelastic material, it is also dependent on other parameters. The geometry, stiffness, mass, and mode shape of the combination of the damping material and the structure to which it is applied will affect the performance of the damping material.
Presently known viscoelastic materials consist of single components or polymer blends. Since presently known single component viscoelastic materials perform over fairly narrow temperature ranges, conventional solutions to wide temperature variations incorporate multiple layers of viscoelastic material, with each layer being optimized for a different temperature range.
Briefly, in one aspect of the present invention, polydiorganicsiloxane oligourea segmented copolymers are provided wherein such copolymers comprise (a) soft polydiorganosiloxane diamine units, hard polyisocyanate residue units, wherein the polyisocyanate residue is the polyisocyanate minus the xe2x80x94NCO groups, optionally, soft and/or hard organic polyamine units, wherein the residues of isocyanate units and amine units are connected by urea linkages, and terminal groups, wherein the terminal groups are functional endcapping groups, and (b) silicate resins. The composition may also optionally contain free radical initiators, silane crosslinking agents, moisture cure catalysts, and nonreactive additives such as fillers, pigments, stabilizers, antioxidants, flame retardants, plasticizers, compatibilizers and the like.
The compositions of the present invention are particularly useful as pressure sensitive adhesives and in one aspect of the present invention, a curable pressure sensitive adhesive composition is provided comprising (a) polydiorganosiloxane oligourea segmented copolymer comprising alternating soft polydiorganosiloxane units and hard polyisocyanate residue units, wherein the residue units are polyisocyanate units minus the xe2x80x94NCO groups, and optionally, soft and/or hard organic polyamine units, wherein the residues of isocyanate units and amine units are connected together by urea linkages and the copolymer has functional terminal groups, and (b) silicate resins.
In another aspect of the present invention, the pressure sensitive adhesives (PSAs) can be used to fabricate PSA articles, wherein the PSA articles comprise a flexible substrate and a layer of PSA prepared in accordance with the present invention. Furthermore, the substrate may be any substrate that would be known to those skilled in the art and may further be coated or treated to provide a low energy release surface on one surface (typical, the backside surface), such as coating with a low adhesion backsize, a release coating and the like, such that the PSA article could be rolled up on itself like a conventional roll of tape. Alternatively, the substrate may be treated or coated with additional layers to provide a tie layer, a primer layer, a barrier layer and the like between the substrate and the adhesive layer.
The present invention further provides vibration damping compositions comprising (a) a curable polydiorganosiloxane oligourea segmented copolymer comprising alternating soft polydiorganosiloxane units, and optionally soft and/or hard organic polyamine units and hard polyisocyanate residue units, wherein the residue units are polyisocyanate units minus the xe2x80x94NCO groups, such that the residues of isocyanate units and amine units are connected together by urea linkages, and the copolymer has functional terminal groups, and (b) silicate resin.
Additionally, the compositions of the present invention are particularly useful as hot melt adhesives and in one aspect of the present invention, a curable hot melt adhesive composition is provided comprising (a) polydiorganosiloxane oligourea segmented copolymer comprising alternating soft polydiorganosiloxane units and hard polyisocyanate residue units, wherein the residue units are polyisocyanate units minus the xe2x80x94NCO groups, such that the hard units and the soft units are connected together by urea linkages and the copolymer has functional terminal groups, and (b) silicate resins.
In another aspect of the present invention, the hot melt adhesives can be used to prepared rods, sheets, pellets and the like that can be subsequently applied in a molten state to produce an adhesive bond between different substrates. The substrate may be any substrate that would be known to those skilled in the art and would be especially useful in adhering low surface energy materials and electronic components.
The present invention also provides a vibration damping composite comprising at least one substrate and at least one layer of the composition of the present invention The substrate may be flexible, stiff, or rigid. Furthermore, the substrate may be any substrate that would be known to those skilled in the art and may further be coated or treated to provide a low energy release surface, such as a coating with a low adhesion backsize, a release coating and the like.
Such composites may be a constrained layer construction, wherein the construction comprises at least one substrate having a stiffness sufficient to cause resonation within the substrate in response to an internal or external applied force and at least one layer of the composition of the present invention. The constrained layer construction preferably has a composite loss factor, tan xcex4 greater than or equal to 0.4 in the temperature range of between about xe2x88x9280 and 150xc2x0 C. and in the frequency range of 0.01 to 100,000 Hz as evaluated by a Polymer Laboratories Dynamic Mechanical Thermal Analyzer Mark II in the shear mode. The useful temperature range depends on both the frequency and the characteristics of the damping composition.
In another aspect, the composite article construction may be such to provide a bi-directional vibration damping constrained layer construction comprising at least two rigid members, and at least one layer of the composition of the present invention. Generally, each rigid member has a stiffness exceeding that of a 0.25 cm steel plate. Preferably, the vibration damping composition has a tan xcex4 greater than or equal to 0.4 in the temperature range of xe2x88x9280xc2x0 C. and 150xc2x0 C. and in the frequency range of 0.1 to 10 Hz, as evaluated by a Polymer Laboratories Dynamic Mechanical Thermal Analyzer Mark II in the shear mode.
Advantageously, shaped articles can be produced, for example, by techniques such as compression molding, injection molding, casting, calendaring and extrusion. Curing can be provided by techniques common for free radical or moisture cure crosslinking reactions.
The compositions of the present invention have excellent physical properties typically associated with polydiorganosiloxane polymers such as moderate thermal and oxidative stabilities, UV resistance, low index of refraction, low surface energy, and hydrophobicity, resistance to degradation from exposure to heat, and water, good dielectric properties, good adhesion to low surface energy substrates, and flexibility at low temperatures. In addition, the compositions exhibit a combination of unexpected properties including, for example, excellent green strength, that is, mechanical strength in the uncured state, allowing subsequent operations to contact the surface before the compositions have cured, controlled flow and crosslinked density characteristics permitting thick coatings on irregular surfaces, good conformability to irregular surfaces, excellent mechanical properties typical of curable systems, excellent damping performance over a broad temperature range, an ability to withstand large strains, excellent adhesion to a variety of substrates when formulated for adhesion, and handling characteristics that permit easy attainment of desired thicknesses and shapes. Furthermore, the compositions can be cured at room temperature, thus permitting use of temperature sensitive substrates.
The compositions of the invention have good resistance to environmental conditions and good performance over a broad range of frequency and temperature. When used as vibration damping materials, the compositions of the present invention have wide utility for minimizing adverse vibration in constrained layer damping treatments as well as minimizing adverse wind sway and seismic influences in buildings subject to wide temperature and humidity variations.
The present invention further provides a process for producing curable compositions comprising (a) forming a polydiorganosiloxane oligourea segmented copolymer by adding at least one polyisocyanate and at least one endcapping agent that has end groups that are reactive under free radical or moisture cure conditions to an organic solvent solution of at least one polyamine, wherein the polyamine is at least one polydiorganosiloxane diamine or a mixture of at least one diorganosiloxane diamine and at least one organic polyamine, mixing the solution and allowing the polyisocyanate, endcapping agents, and polyamine to react to form a polydiorganosiloxane oligourea segmented copolymer, (b) blending the polydiorganosiloxane oligourea segmented copolymer solution with at least one silicate resin, and (c) removing the organic solvent.
The present invention still further provides a process for preparing curable compositions comprising the steps of continuously providing reactants, wherein the reactants comprise at least one polyisocyanate, at least one polyamine, and at least one endcapping agent to a reactor; mixing the reactants in the reactor; allowing the reactants to react under substantially solvent free conditions to form a polydiorganosiloxane oligourea segmented copolymer; conveying the copolymer from the reactor; providing the copolymer, at least one silicate tackifying resin, and solvent to a second reactor; mixing the copolymer, the silicate tackifying resin, and the solvent in the second reactor to form a tackified composition; and conveying the tackified composition from the second reactor.
The present invention still further provides an essentially solventless process for producing curable compositions comprising (a) forming polydiorganosiloxane oligourea segmented copolymer by continuously providing reactants, wherein the reactants comprise at least one polyisocyanate, at least one endcapping agent that has end groups that are reactive under free radical or moisture cure conditions, and at least one polyamine to a reactor, mixing the reactants in the reactor, allowing the reactants to react to form a polydiorganosiloxane oligourea copolymer, and conveying polymer from the reactor and (b) incorporating a silicate resin by blending the silicate resin with reactants or the polydiorganosiloxane oligourea segmented copolymer.
This solventless process is environmentally advantageous as there are no solvents to be evaporated from the final composition. The continuous nature of this process has several other inherent advantages over conventional solution polymerization processes. The material can be extruded into a variety of shapes immediately subsequent to polymerization which obviates the degradation, which may be associated with additional heat from further reprocessing steps. Another advantage of this substantially solventless, continuous process is the ability to add or blend, in line, the silicate resin, as well as various free radical initiators, silane crosslinking agents, moisture cure catalysts, and nonreactive fillers, plasticizers other polymers, and other property modifiers into the polydiorganosiloxane oligourea segmented copolymer before, during, or after formation of the copolymer.
Optionally, nonreactive additives such as fillers, plasticizers, pigments, stabilizers, antioxidants, flame retardants, compatibilizers and the like may be added at any point in each of the above processes.
Each process of the present invention has unique advantages. The solvent process permits the use of conventional solvent coating equipment while resulting in curable tackified compositions whose high green strength, i.e., strength prior to curing, permits subsequent manufacturing operations before cure. The solventless process permits thick coatings onto irregularly shaped surfaces, use of conventional hot melt coating equipment with lower processing temperatures than typically used with conventional hot melt processable compositions, the advantage associated with high green strength, as well as many advantages involving the environment, economics, and safety that are associated with a substantially solventless process. The combination of elements of each process permits one to customize the silicate tackifying resin concentration at a later date for specific applications while retaining some of the advantages of each.